How is it used? Tuberculosis ( TB) screening tests are not used as general population screens but are used to screen people who are at high risk for TB exposure, such as: People with diseases or conditions that weaken the immune system, such as HIV or AIDS, which makes them more vulnerable to a TB infection Those who are in confined living conditions such as homeless shelters, migrant farm camps, nursing homes, schools, and correctional facilities Healthcare workers and others whose occupations bring them in close contact with those who may have active TB Those who have been in close contact with someone who has an active case of TB People who have signs and symptoms consistent with active tuberculosis Those who come from or have lived for a period of time in a foreign country where TB may be more common Those who inject illegal drugs TB screening tests are also used sometimes as part of a routine examination prior to starting school or a new job. Since mothers can pass TB to their unborn children, pregnant women are sometimes screened. Either a tuberculin skin test ( TST) or an interferon gamma release assay ( IGRA) may be performed to screen for TB: The tuberculin skin test involves two steps: the injection of a small amount of purified protein derivative ( PPD) solution under the first layer of skin of the forearm and an evaluation of the injection site conducted by a health practitioner at 48 and/or 72 hours to see if a local skin reaction has occurred. The IGRA test measures the release of a substance called gamma interferon by white blood cells in a sample of blood when the cells are exposed to specific TB antigens. The IGRA test is not performed by all laboratories. The test requires viable white blood cells, so the IGRA blood sample must be received and tested by a laboratory within a designated window of time. Recommendations from the Centers for Disease Control.
A tuberculin skin test is done to see if you have ever had tuberculosis ( TB). The test is done by putting a small amount of TB protein (antigens) under the top layer of skin on your inner forearm. If you have ever been exposed to the TB bacteria ( Mycobacterium tuberculosis your skin will react to the antigens by developing a firm red bump at the site within 2 days. The TB antigens used in a tuberculin skin test are called purified protein derivative ( PPD). A measured amount of PPD in a shot is put under the top layer of skin on your forearm. This is a good test for finding a TB infection. It is often used when symptoms, screening, or testing, such as a chest X-ray, show that a person may have TB. A tuberculin skin test cannot tell how long you have been infected with TB. It also cannot tell if the infection is latent (inactive) or is active and can be passed to others. Why It Is Done A tuberculin skin test is done to find people who have tuberculosis ( TB including: People who have been in close contact with someone known to have TB. Health care workers who are likely to be exposed to TB. People with TB symptoms, such as an ongoing cough, night sweats, and unexplained weight loss. People who have had an abnormal chest X-ray. People who have had a recent organ transplant or have an impaired immune system, such as those with human immunodeficiency virus ( HIV). A tuberculin skin test should not be done for people: With a known TB infection. Who have had a previous severe reaction to the TB antigens. Who have a skin rash that would make it hard to read the skin test. How To Prepare Before having a tuberculin skin test, tell your doctor if you: Have symptoms of tuberculosis ( TB such as an ongoing cough, night sweats, or unexplained weight loss. Have had a severe reaction to a tuberculin skin test in the past. Have had TB in the past. Have risk factors for TB, which are things that.
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